In 3GPP, LTE-advanced as a developed version of LTE has been considered, giving consideration of a wireless interface efficiently covering a local area such as an indoor facility where a large volume of traffic is concentrated in addition to a cell layout centered on a conventional macro cell. Along with this, a heterogeneous network (HetNet) for deploying a low transmission power cell (small cell), such as a pico cell or a femto cell, within a macro cell has been considered. It is desired that the frequencies of the macro cell and the low transmission power cell be the same in terms of the frequency usage efficiency in the HetNet environment. However, in this case, there arises a problem of inter-cell interference between the macro cell and the small cell.
When the small cell is a pico cell, a method is under consideration in which a technique called Cell Range Expansion (CRE) is applied for the purpose of load distribution from a macro base station to cause a macro terminal (MUE) outside of the coverage of the pico cell to attach to the pico cell. As shown in FIG. 11, a terminal (PUE) to attach to a pico cell outside the coverage of the pico cell by the application of CRE experiences large interference from the macro cell. Particularly, interference from a control channel of the macro cell to a control channel to the PUE has become a problem (see FIG. 12), and various interference control methods have been considered. As one of the methods, there is a method of providing a blank area (Almost blank subframe: ABS) in a specific subframe to be transmitted from the macro cell to reduce interference with the pico cell (see FIG. 13).
Further, in a system using carrier aggregation (CA) for aggregating LTE compatible frequency bands (component carriers) to realize a wider bandwidth, the application of cross carrier scheduling is considered to reduce interference between a macro cell and a small cell (see Non-Patent Document 1). The cross carrier scheduling is a technique in which, when secondary cells (SCell) of frequency bands different from a primary cell (PCell) of a certain frequency band are aggregated to perform communication, SCell control information is notified from a control channel of the PCell to eliminate the need for the control channels of the SCells. A subframe pattern to which this cross carrier scheduling is applied is set individually for each UE.
The application of this cross carrier scheduling can mitigate interference from a macro cell to the control channel of a pico cell at a SCell frequency (secondary frequency) of the macro cell the control channel of which is unnecessary. On the other hand, at a secondary frequency of a pico cell the control channel of which is unnecessary, there is no need to care about interference from the control channel of the macro cell. Thus, it is desired in the system using the carrier aggregation to deploy a PCell of macro cell and a PCell of pico cell in such a manner to make the frequencies thereof different from each other as shown in FIG. 14 in order to reduce interference between the macro cell and the small cell. In other words, a SCell of pico cell is deployed for a PCell of macro cell, and a PCell of pico cell is deployed for a SCell of macro cell.